The present invention relates to a platform that is selectively elevatable by operation of a scissor-type jack. The jack is extended and retracted by a power actuator.
Scissor jacks for elevating work platforms and objects are well know in the art. One such device is shown in U.S. Pat. No. 5,355,711. This jack is part of a vehicle lift used in chassis straightening. This type of scissor jack utilizes a power actuator 36 attached to a plurality of bars arranged in an X pattern with a pair of bars. Each pair of bars is positioned on a respective opposite side of the work platform. One end of each of the four bars is secured either to the lift platform or to a base frame. One bar in each of the pairs of bars has the actuator connected thereto and the other end of the bar attached to the work platform. The other bar of each pair of bars has one of its ends mounted for movement relative to the floor. The X bar arrangements, through extension of the actuator, will elevate the platform and retraction of the actuator lowers the platform. Such an arrangement of bars results in the pivot point 27 between the two bars in each pair moving laterally during extension and retraction which also moves the center of the support provided for by the jack under the platform. Another problem with the type of jack shown in U.S. Pat. No. 5,355,711 is that the arrangement of bars and power actuator limit how low the platform can be lowered.
Another type of scissor jack is made by Southworth and available as Model No. A-350W. This scissor jack is a double X arrangement with one X stacked on top of the other, i.e. in the direction of extension for lifting and retraction for lowering. A similar jack is available from Dayton and can be found in the Grainger Catalog #391 as Stock No. 3KR47. In this latter jack, the center between the support points with the platform also moves laterally with elevation of the platform.
Another type of scissor jack is operated by a screw and a manually operated crank handle and is available typically as an automobile jack used for changing tires. This type of jack uses a base, a car engaging top platform and four bars on each side of the jack, two lower bars on each side being connected to the base (forming an upwardly diverging V), two upper bars on each side being connected to the work platform (forming a downwardly diverging V). Further, the upper and lower two bars on each side are pivotally connected to one another. In this type of jack, the center of support does not move laterally during extension and retraction of the jack.
Thus, there is a need for an improved elevatable platform utilizing a scissor-type jack in which the center of the jack moves along a path generally parallel to the direction of movement of the load engaging platform and that provides a low profile when retracted.
The present invention involves the provision of a jack device adapted for use to apply a force or support a load and move the load between a lowered position and an elevated position. The device includes an improved scissor jack that when in its lowered or retracted position will provide a compact profile in height. The jack has an arrangement of bars that maintains a center of movement along a common center line that is generally parallel to the direction of extension of the jack. The jack utilizes a double X arrangement of bars which arrangement has a longitudinal axis generally transverse to the direction of extension of the jack in the load applying direction. Free ends of the bars forming the two X""s contact either a base or the load engaging platform for supporting the platform above the base. The other ends of the bars are mounted for pivotal movement either to the base or to one another. The bars forming each X are pivotally connected to one another. The free ends of the bars in each X may be provided with rollers to reduce friction during extending and retracting movement of the jack. A power actuator is connected between the two X""s and is operable to expand and contract the double X arrangement to extend and retract the platform. A safety latch can be provided to ensure that the jack remains at a desired extended position in the event the power actuator should fail. The safety latch may be operated remotely by the actuation of another power actuator. The platform may be a relatively large platform utilizing a plurality of the jacks, say for example four. Such an arrangement would be particularly useful for an automotive straightening bench.